This invention is related to and an improvement over U.S. patent applications of H. J. MacKenzie entitled IMPLEMENT LEVEL LIFT SYSTEM, Ser. No. 156,892, and Ser. No. 156,890, of W. C. Swanson entitled IMPLEMENT LEVEL LIFT SYSTEM WITH REPHASING VALUES, which applications have a filing date and assignee in common with this application.
Uniformly raising and lowering what are commonly called folding wing implements, such as multi-sectioned frame members of large disk harrows and cultivators, has long been a problem. The prior art attempts have tended to concentrate on the use of two sets of master-slave cylinders or rams. One end of each master cylinder was pivotally connected to the center or middle frame of the implement and the other ends thereof were connected by a lever system to a rock shaft to which the implement wheels were connected. The piston or head ends of the master cylinders were hydraulically connected in parallel and rod end of each master cylinder was independently hydraulically connected in series to the head end of the slave cylinder. The slave cylinders were each physically connected to a carrying wheel mounted on each of the wing frames. With the proper ratios of master rod chamber volume to slave head chamber volume, the wing frames would theoretically lift uniformly with the middle frame. The many deficiencies of the master-slave arrangement have been recited in the aforementioned co-pending applications and reference may be made thereto for a more complete understanding. However, even if these master-slave systems functioned perfectly, the volume of the master rod chamber had to equal the slave head chamber volume, assuming the linkage connecting the cylinders to the wheels was the same. Such an arrangement places a limitation on the implement designer which often increases cost because non-standard cylinders often have to be utilized on the implement.
It is, therefore, an object of this invention to provide a hydraulic circuit for synchronous lift of folding wing implements which permits use of standard size and conventional lift cylinders or rams.
It is also an object of this invention to provide such a hydraulic circuit which is capable of rephasing or synchronizing the lift rams, which rephases rapidly and efficiently, and which controls the maximum drop rate of the implement.
It is another object to provide such a hydraulic circuit which assures that the wing frames initiate their lowering at the same time as the center frame.